Device for use in percussion mechanisms



United States Patent 3,250,335 DEVICE FOR USE IN PERCUSSION MECHANISMS Karl Evert Anders Joelson, Box 1054, Brastad, Sweden Filed Aug. 11, 1964, Ser. No. 388,909 Claims priority, application Sweden, Aug. 21, 1963,

12 Claims. (:1. 173-439 The present invention concerns an arrangement for use in percussion mechanisms which include a movable working piston in a cylinder, During its working stroke this working piston moves toward a tool, a working surface, or the like under the influence of a suitable driving mechanism such as an eccentric, a spring, or a hydraulic mechanism. Such percussion mechanisms or tools are used in drills (rock drills), hammers or tapping machines for example. It often happens during operation of these machines that the machine bounces back so that the piston does not contact the working tool. This also occurs for example when the operator tries to loosen a wedged drill or tapping bar. In this case the machine is withdrawn or lifted upward simultaneously with operating. To prevent damage to the machine in cases such as described above, it is necessary that the kinetic energy in the piston during the latter part of its working stroke must be to a large extent absorbed softly. It is hardly possible to allow the piston to strike a fixed stop surface since this surface would soon be destroyed under the impact of the blows.

This disadvantage is avoided according to the present invention by furnishing the percussion mechanisms with a flexible or elastic clamping arrangement which captures and absorbs the pistons energy at the end of the working stroke if the piston does not strike or is not stopped by the intended working tool. The damping effect of the device may be adjustable, and the damping device arrangement is preferably of the hydraulic type having a chamber in which the damping fluid is constructed by a narrow duct.

Another problem which accompanies this type of percussion mechanism is the return of the piston to its starting position after a working stroke. It has been found advantageous to return the piston without using any mechanical device such as a spring. On the other hand, hydraulic return mechanisms are quite complicated and expensive and also have the disadvantage that the amount of liquid which must be displaced during the working stroke exerts a substantial braking eifect. According to the present invention the disadvantages of presently known return mechanisms are avoided by exposing one side of the piston to a low pneumatic pressure (vacuum) and/or exposing its other side to a higher or a superatmospheric pressure,

The invention can be utilized advantageously with different types of percussion mechanisms. For example the percussion mechanism may have a hydraulically driven piston or have a mechanical stroke arrangement with hydraulic power transfer from a pump unit to the machines striking mechanism itself. The striking mecha nism of these machines can be mechanical or include pneumatic transmission from a primary piston to a striking piston in a known way.

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One embodiment of the invention is shown schematically in cross-section in the accompanying drawing.

The embodiment shown in the drawing includes an outer, closed space or housing 1, which is mainly filled with a pressurized'fluid supplied from container 11 by means of a pump 14 and line 15 in a way described be low. A cylinder 6, which is also filled with fluid, is 10- cated inside the housing. At one end of the cylinder there is a driving piston 4 which may for example be driven by rotatable driving means such as an eccentric 2 or other suitable means. The eccentric 2 may be connected to a flywheel 3 and may be driven by a hydraulic motor 2a through drive shaft 2b. At the opposite end of cylinder 6, in cylinder section 8a, there is a working piston or striking piston 8. This working piston is sealed with cylinder 6 by means of packing ring 10. In the illustrated embodiment the piston 4 may be returned to its starting position by a spring 7. The working piston 8 is shown in its starting position and is returned to this position by a vacuum pressure acting on its upper side. This is achieved by connecting pipe 16 to a vacuum source. This pipe 16 may include a check valve 17. The vacuum source may for example comprise an ejector 18 which may be installed outside the housing 1. Pump 14 pumps fluid from container 11 through pipe 15 to hydraulic motor 2a and from there via conduit 21 through ejector 18 and conduit 22 into housing 1 from which the fluid is returned to container 11 via return conduit 23. Vacuum pressure occurs in pipe 16 in a known way when fluid flows through the ejector, whereby the pressure of the atmosphere acting on the lower side of the piston 8 raises the piston into the position thereof shown in the drawing.

Cylinder 6 may communicate with the outer housing or envelope 1 through a passage furnished withcheck valve 5 and through outlet 9 communicating with passage 19 or through passages or grooves 12 and 13 arranged in driving piston 4 and the walls of cylinder 6 respectively. One of the grooves 12 or 13 may be helically shaped so that the position at which these two grooves communicate with each other can be adjusted, for example by rotating driving piston 4. Working piston S has a smaller diameter than driving piston 4 and, correspondingly, the section of cylinder 6 through which working piston 8 moves has a smaller diameter than the section of cylinder 6 through which driving piston 4 moves.

In order to capture and absorb the kinetic energy at the end of a working stroke, if the piston does not strike working tool 24, the percussion mechanism is furnished with a damping device. According to the illustrated embodiment the damping device comprises a light casing 25 slideably mounted in cylinder 8a which is carried by piston S. The casing is sealed against the piston at the large diameter portion 26 and at a smaller diameter portion 27. Space 28 communicates through axial passage 29 with the drive fluid in the housing. During each working stroke of piston 8 the drive fluid tends to urge the casing 25 downward. However the casing can only be urged so until it bumps against a stop ring 30 located around piston section 27. Suitably this stop ring can consist of a steel ring divided into two halves which are mounted in a groove around the periphery of the piston and held together by a spring ring,

If the piston S, 26, 27 moves downward without concooler.

tacting working tool 24, the damping casing 25 is stopped by a collar 31 in the machine housing. Since the casing 25 has little weight, no damage is done to it or to the housing. The fluid in space 28 is discharged at a controlled speed out through duct 29 and thereby the piston Will be steadily braked. The character of the braking may be changed as desired by giving duct 29 dilierent diameters. The passage area of the duct may be adjustable by including an adjusting means such as an adjustable valve, not shown. On the next working stroke space 28 is filled by driving fluid which is supplied through passage 29 and the damping casing 25 is returned to its position against stop ring 30.

The remainder of the arrangement functions in the following way. When eccentric 2 rotates, the driving piston 4 is urged downward at a normal speed of about 1 to 1.5 meters/ sec. for example. At thesame time check valve 5 is closed by the pressure created in cylinder 6 by the movement of the driving piston. This pressure also presses working piston 8 downward. Since the section of the working piston in cylinder 6 has a smaller diameter than driving piston 4, the working piston moves at a higher speed, for example 8 meters/sec. Both pistons attain their approximately maximum speed when the eccentric has rotated 90. At this moment the working piston 8 will strike against the working tool or working object 24, while the eccentric 2 continues to force the driving piston downward at decreasing speed. When the working piston 8 reaches its maximum speed and contacts the working objects 24, outlet 9 is uncovered or passages 12, 13 are joined whereby the working piston is no longer driven for-ward but instead the working piston 4 will press the hydraulic fluid out into the outer housing 1. During the return stroke of driving piston 4 the check valve 5 is opened and fluid will fill the cylinder space 6.

Since the larger part of the power output of the driving piston occurs during a 90 rotation of the eccentric from the home position, it is appropriate to connect the eccentric to a flywheel 3 in order to store the surplus energy. During the eccentrics rotation from 180 to 360 piston 4 is returned by spring 7 and piston 8' is returnedby the low pressure in pipe 16. Cylinder 6 may be put in communication with the outer envelope 1 when the pistons 4 and 8 attain maximum speeds whereby the working piston 8 is released or disengaged and becomes independent of the continued movement of the driving piston 4. The disengaging position can be chosen arbitrarily and can also be variable for example by using the grooves or passages 9, 12, 13 described above.

The vacuum or air pressure in cylinder 8a may suitably act continually on piston 8, but by using a valve it can be arranged so that the vacuum or air pressure acts only when the piston is to be returned at the end of a stroke. Since the pressure fluid is circulated from container 11 through the hydraulic motor, the ejector, the fluid space in envelope 1 and the ring-shaped space of the damping casing, a cooling of the pressure fluid may be obtained by a separate The ejector may be mounted anywhere in the fluid stream where the speed of the stream is suflicient to achieve the desired low pressure on the suction side of the ejector. It is not necessary to provide the check valve 17 in pipe 16 between the ejector and cylinder 8a but such a check valve is advantageous in order to prevent the fluid from reaching the upper side of piston 8 when the pump unit is stationary and also to prevent the fluidv from being sucked down to the piston if the piston, during the last part of the working stroke, creates a greater vacuum than that produced by the ejector.

The ejector 18 may also be provided in or connected with the exhaust conduit from an internal combustion engine which rotates the eccentric 2.

What I claim is:

1. A percussion mechanism comprising a cylinder, a working piston slide-ably mounted in said cylinder, driving means for driving said Working piston, a damping means movably mounted with respect to said piston to form a fluid containing damping chamber between said working piston and said damping means, and means conecting said chamber to a fluid source outside said chamber.

2. A percussion mechanism according to claim 1 wherein said connecting means is a duct passing through said piston.

3. A percussion mechanism according to claim 1 wherein said conecting means connects said chamber in a fluid system which also drives said working piston.

4. A percussion mechanism according to claim 1 wherein the movement of said dampingmeans with respect to said piston is limited by stop means on said piston.

5. A percussion mechanism comprising a cylinder, a working piston slideably mounted in said cylinder, driving means for driving said working piston, a damping means slideable with respect to said piston and surrounding two portions of said piston, said two portions of said piston.

having different diameters and said damping means being sealed against'said two portions to form a fluid containing damping chamber between said working piston and said damping means.

6. A percussion mechanism comprising a cylinder, a working piston slideably mounted in said cylinder, driving means for driving said working piston, a damping means movably mounted with respect to said piston to form a fluid containing damping chamber between said working piston and said damping means, and stop means fixedly secured to said cylinder and in the path of said damping means to stop the motion of said damping means when the working piston approaches the end of its working stroke without contacting its intended working object.

7. A percussion mechanism comprising a cylinder, a working piston slideably mounted in said cylinder, driving means for driving said working piston, hydraulic damping means to gradually slow the movement of the working piston at the end of its working stroke if the working piston is not stopped by contact with its intended working object, at least one liquid flow operated ejector whose suction side is connected to said cylinder to return said piston to its starting position after its working stroke is completed, and hydraulic pump means to circulate liquid through said hydraulic damping means and said ejector.

8. A device for use in a percussion mechanism, said device comprising a cylinder, a piston slidably mounted in said cylinder, a damping means movably mounted with respect to said piston to form a fluid containing damping chamber between said piston and said damping means, and stop means fixedly secured to said cylinder and in the path of said damping means to stop the motion of said damping means when the piston approaches the end of its movement path in the cylinder.

9. A device for use in a percussion mechanism, said device comprising a cylinder, a piston slidably mounted in said cylinder, a damping means slidable with respect to said piston and surrounding two portions of said piston, said two portions of said piston having difierent cross sectional areas and said damping means being sealed against said two POI'tiLIlS to form a fluid containing damping chamber between said piston and said damping means.

10. A percussion mechanism comprising a cylinder, a piston slidably mounted in said cylinder, hydraulic damping means to gradually slow the movement of the piston at the end of its movement path in the cylinder, at least one liquid flow operated ejector whose suction side is connected to said cylinder to return said piston to its initial position, and hydraulic pump meansto circulate liquid through said damping means and said ejector.

11. A percussion mechanism comprising a cylinder connected to a vacuum source located outside said cylinder, a working piston slidably mounted in said cylinder, driving means for driving said working piston, fluid damping means to gradually slow the movement of the working piston at the end of its working stroke if the working piston is not stopped by contact with its intended working object, and pneumatic means for returning said piston to its starting position after its working stroke is completed.

12. A percussion mechanism according to claim 11 wherein said vacuum source comprises at least one liquid flow operated ejector.

References Cited by the Examiner UNITED STATES PATENTS MILTON KAUFMAN, Primary Examiner. 

1. A PERCUSSION MECHANISM COMPRISING A CYLINDER, A WORKING PISTON SLIDEABLY MOUNTED IN SAID CYLINDER, DRIVING MEANS FOR DRIVING SAID WORKING PISTON, A DAMPING MEANS MOVABLY MOUNTED WITH RESPECT TO SAID PISTON TO FORM A FLUID CONTAINING DAMPING CHAMBER BETWEEN SAID WORKING PISTON AND SAID DAMPING MEANS, AND MEANS CONECTING SAID CHAMBER TO A FLUID SOURCE OUTSIDE SAID CHAMBER. 